The present disclosure concerns Reed-Solomon decoders that are arranged and constructed to adapt decoding operation to, for example, better accommodate varying channel conditions.
Reed-Solomon decoders are known. The literature shows the concept of soft-decision receivers, in particular erasure Reed-Solomon decoders. Various algorithms for erasure decoding are also known. Generally erasure decoding is a process of decoding that uses in addition to a received code word certain channel quality information corresponding to the symbols of the code word. The expectation is that when the channel quality is low the likelihood of an error is high. A symbol in the code word with a corresponding low or poor channel quality is often referred to as an erasure. It has been shown that a soft decision receiver is capable of correcting up to twice as many channel induced errors as a hard decision receiver, provided the channel quality information is reliable.
In any event one erasure algorithm, described along with others in Error Control Systems for Digital Communication and Storage, by Stephen B. Wicker. Prentice Hall, 1995, is Euclid""s algorithm for erasure Reed-Solomon decoding. This algorithm is expected to reduce the computational intensity of a soft-decision receiver to a level comparable with a hard-decision receiver (for codes up to the order of about 40 symbols per code word). This algorithm requires as inputs a received code word, a list of erasures and two parameters, one indicating how many erasures are provided and one indicating up to how many errors to correct. Increasing one of the parameters requires that the other be decreased.
The above notwithstanding soft decision receivers have not gained wide acceptance in communications systems and equipment that must operate with widely varying channel characteristics, such as encountered in wireless communications. Generally a wireless channel will experience additive white guassian noise and extreme variations in channel loss. These variations in channel loss are caused, in some cases by differences in effective channel length and more often by fading caused by multiple signal paths and the Doppler effect.
Additionally the errors resulting from additive white guassian noise are randomly located within the code word and may not be highly correlated with observed channel quality. This type of error is more readily corrected using the inherent error correcting capability of a Reed-Solomon code rather than a soft decision or erasure Reed-Solomon approach. Said another way we should increase the parameter indicating number of errors to correct in for example the Euclid algorithm. On the other hand errors resulting from channel fades tend to be grouped together and highly correlated with observed channel quality. These errors are readily corrected as erasures, so we should increase the parameter indicating number of erasures. However as noted above increasing one parameter means decreasing another. This problem has resulted in reluctance on the part of practitioners to use this form of decoder, notwithstanding the theoretical 2xc3x97 potential improvement in error correcting ability.
Clearly a need exists for an adaptable Reed-Solomon decoder and methods thereof suitable for use in a soft decision receiver with varying channel characteristics.
This invention is directed to an adaptive soft decision receiver including an adaptive Reed-Solomon decoder and corresponding method of adaptively decoding a Reed-Solomon(RS) encoded channel that is arranged and constructed to demodulate and decode a RS(n,k) encoded symbol stream. The receiver includes a symbol detector coupled to the channel for detecting channel symbols and providing a corresponding code symbol stream and the adaptive Reed-Solomon decoder. The adaptive Reed-Solomon decoder executes the aforementioned method and includes a code register, coupled to the symbol detector, for storing a received code word including n code symbols, an index register, coupled to the symbol detector for storing a location information corresponding to a portion of the code symbols, a processor, coupled to the code register and the index register, for performing soft decision decoding using an error parameter and an erasure parameter to provide corrected data when the soft decision decoding is successful and to provide a failure indication when the soft decision decoding is unsuccessful, and a controller, coupled to the processor, for providing the error parameter and the erasure parameter and for adjusting the error parameter and the erasure parameter when the processor provides the failure indication.